CGP 6085A [4-(5,6-dimethyl-2-benzofuranyl) piperidine HCl] is reported to be a potent serotonin uptake inhibitor. We attempted to characterize the effects of this drug on the rat brain stem and hypothalamus. In the course of our studies, we observed that CGP 6085 A is a potent inhibitor of monoamine oxidase both in vivo and in vitro. In characterizing the blood pressure effects of this drug, it appears that CGP 6085 A has hypotensive properties in acute studies when measured by direct intraarterial catheterization in the urethane anesthetized rat and awake canulated rat. These effects may be linked primarily to its ability to inhibit monoamine oxidase. The approximately 20 mm drop in blood pressure appears to be due to inhibition of brain stem monoamine oxidase as other 5HT uptake inhibitors citalopram and fluoxetine do not exhibit a similar hypotensive action. In addition, CGP 6085 A appears to produce a hypothermic effect, principally by altering hypothalamic serotonin uptake. Citalopram and fluoxetine were equally as potent as CGP 6085 A in these experiments in reducing core temperature in the rat.